1. Field of the Invention
This invention relates to a method and apparatus for the production of a cast article having a small hole. More particularly, this invention relates to a metal mold casting technique, particularly to a small hole forming technique usable in the production of a molded article having a small hole by metal mold casting of an amorphous alloy (metal glass), particularly an optical connector parts such as a ferrule and a capillary.
2. Description of the Prior Art
As a typical example of a molded article which has a small hole and which requires high dimensional accuracy, a ferrule or capillary of an optical connector may be cited.
Now referring to the attached drawings for explanation, FIG. 1 illustrates one mode of the optical connector ferrule 10 of a one-piece construction comprising a capillary part 11 and a flange part 12. Specifically, this ferrule 10 is composed of the capillary part 11 which has formed along the axis thereof a through-hole 13 of a small diameter intended for the insertion of an optical fiber 17 (or the basic thread of an optical fiber coated with a plastic thin film) and the flange part 12 which has formed along the axis thereof a through-hole 14 of a large diameter intended for the insertion of a sheathed optical fiber 16 (the optical fiber coated with a sheath). The through-hole 13 of the small diameter and the through-hole 14 of the large diameter are connected into each other through a tapered part 15. The connection of a pair of optical fibers 17, 17 is attained by inserting into a split sleeve 18 through the opposite ends thereof the ferrules 10, 10 having the optical fibers already inserted and joined therein and then abutting the end parts of the ferrules 10, 10. As a result, the optical fibers 17, 17 are allowed to have their leading ends abutted and joined in a state having the axes thereof aligned to each other.
FIG. 2 illustrates another mode of the optical connector ferrule 10a comprising a capillary part 11a and a flange part 12a as separate components.
The diameter of the small hole into which the optical fiber is inserted depends on the type of ferrule. For instance, the capillary (ferrule) of the SC type has a small hole of 0.126 mm in diameter and 10 mm in length.
Heretofore, the ferrules are manufactured by using ceramics such as zirconia. The formation of a small hole in the ferrule is attained by preparatorily forming a ceramic ferrule blank having a relatively smaller hole by injection molding, calcining the ceramic ferrule blank, and then subjecting the calcined ceramic ferrule blank to wire lapping thereby finishing it to a specified dimension. Furthermore, the production of the ceramic ferrule comprises, besides the above inside diameter finishing, many steps of machining such as abrasive finishing of the outside diameter and polishing of the leading end into the spherical convex surface (PC polishing). Accordingly, the process of production is lengthy and the cost of production is inevitably large.
As a method capable of solving the problems mentioned above, the assignee of this application has proposed a method which, by the combination of the conventional technique based on the metal mold casing method with an amorphous alloy exhibiting a glass transition region, allows an amorphous alloy molded article satisfying a predetermined shape, dimensional accuracy, and surface quality to be mass-produced with high efficiency by a single process, even when the article is that having a small hole such as an optical connector ferrule or an article having a complicated shape (Japanese Patent Application, KOKAI (Early Publication) No. 10-186176). In the method for the production of the amorphous alloy molded article having a small hole disclosed in this patent literature, basically the formation of the small hole is effected by injecting a melt of a material capable of producing an amorphous alloy into a mold cavity having a core pin set therein at a high speed and thereafter the core pin is drawn from the resultant cast product to form a small hole.
To manufacture a cast article having a small hole, usually a core pin uniformly coated with a release agent should be used. Since the release agent used evaporates rapidly when the molten metal contacts the core pin, however, bubbles or blemishes remain in the cast article. Furthermore, the direction of evaporation of the release agent can not be uniformly and constantly controlled, which poses the problem that the dimensional accuracy of the small hole portion can not be heightened to a desired level. Conversely, when the injection pressure during the casting is increased to obtain the cast article with high accuracy, other problems will be incurred that the core pin can not be drawn out from the cast product because any gap will not remain between the cast material and the core pin for forming the small hole. Further, this process has the problem of exposing the core pin to the possibility of sustaining scarring in its surface or even breakage during the casting or during the operation of drawing of the core pin after casting. Since the core pin is made of a sintered hard metal or cemented carbide and thus expensive, the fact that the scarred or broken core pin can not be used repeatedly forms a large factor for boosting the production cost of the article.
Such problems are not particular to the optical connector ferrule or capillary, but common to the metal mold casting of a metal molded article having a small hole.
It is, therefore, a fundamental object of the present invention to provide a method and apparatus capable of producing a cast article having a small hole at low cost with high productivity in a short time, which can diminish various problems caused by the difficulty of drawing of a core pin from the cast product after the casting or the durability of the core pin as mentioned above.
A further particular object of the present invention is to provide a method and apparatus which allow a molded article satisfying a predetermined shape, dimensional accuracy, and surface quality to be molded by a simple process even when the article is an amorphous alloy molded article having a slender hole and, therefore, enable to provide an inexpensive amorphous alloy molded article having a small hole and excelling in the durability, mechanical strength, resistance to impact and the like, particularly an optical connector part such as a ferrule or capillary.
To accomplish the object mentioned above, the first aspect of the present invention provides a method for the production of a cast article having a small hole.
The first embodiment of the method according to the present invention is characterized by the fact that in the casting of a molten metal into a cavity of a metal mold having a linear core member of a desired cross-sectional shape preparatorily set therein to produce a cast product, a linear core member having a surface film formed by surface coating or by subjecting to a surface treatment is used as the linear core member, and the linear core member is drawn out from the cast product after the casting, thereby forming in the cast product a small hole of the cross-sectional shape substantially equal to that of the linear core member. In this case, the preferred mode is constructed so that a part or the whole of the surface film is peeled off the surface of the linear core member upon drawing it from the cast product after the casting, thereby enabling the linear core member to be drawn from the inside of the cast product.
The second embodiment of the method of the present invention is characterized by the fact that in the method comprising injecting a molten metal into a cavity of a metal mold having a linear core member of a desired cross-sectional shape preparatorily set therein to produce a cast product and drawing out the linear core member from the cast product to form a small hole having the cross-sectional shape of the linear core member, the linear core member is so constructed as to elastically deform in the drawing direction to have a diameter smaller than the original diameter upon drawing the linear core member from the cast product after the casting, thereby enabling the linear core member to be drawn from the inside of the cast product.
The second aspect of the present invention provides an apparatus for the production of a cast article having a small hole characterized by comprising a metal mold provided with a cavity which defines the outer shape of an article, a movable cylindrical guide member having a center bore and disposed in the mold slidably so as to project into and draw back from the cavity, and a linear core member to be set in the mold via the center bore of the cylindrical guide member, and preferably further means for applying a tension load, preferably not more than 1960 N/mm2, to the linear core member in its longitudinal direction.
By using the method and apparatus mentioned above, it is possible to manufacture a cast article having a small hole, particularly an amorphous alloy moled article, more particularly an optical connector ferrule or capillary, with high productivity.